(1) Field of the Invention
The present invention relates to telephone switching systems and more particularly to a circuit for determining the class of service of a telephone subscriber station.
(2) Description of the Prior Art
The series 100 Director System electronic translator producted by GTE Automatic Electric identifies the class of service of a connected subscriber station through use of a 28 volt, 80 microsecond pulse on the "C" lead of the subscribers line equipment. All subscriber stations are assigned a particular time slot during which their class of service pulse appears. Also, all subscribers of a particular class of service, for example, metro, nonmetro, pay station, dial pulse, touch call, etc., are connected to a particular class of service detector circuit. Thus, when a subscriber station goes off-hook the director system assigns an available register-sender to the subscriber station. The register-sender applies the 28 volt class of service pulse to the subscriber line equipment which is strapped to gate that pulse to the class of service detector associated with the particular class of service of the subscriber station. The director system includes 100 register senders which generate the class of service pulse on a time division basis. Thus, the director system determines the class of service of a particular subscriber station by associating the output signal of a particular class of service detector with the time slot assigned to a particular subscriber station.
A problem experienced with the director system occurs when a Strowger Automatic Toll Ticketing system, also produced by GTE Automatic Electric, is connected to the director system. This SATT system also causes pulses to appear on the "C" lead of a subscriber's line circuit since it applies 60 volt SATT detection battery to the "C" lead for 200 to 300 milliseconds. Thus a class of service detector must be able to distinguish between valid class of service pulses and pulses generated in response to SATT detection battery. Since class of service pulses can be generated in the presence of SATT detection battery the class of service detector must also detect the presence of a valid class of service pulse appearing simultaneously with the SATT detection battery.
The current state of the art for a class of service detector for the series 100 Director System is represented by GTE Automatic Electric's H-840123-A circuit. However this circuit is unable to distinguish between class of service pulses and SATT pulses and thus has a tendency to produce false class of service detection outputs when SATT detection battery is present.
Accordingly it is the object of the present invention to provide a class of service detector circuit which can detect class of service pulses, discriminate between such pulses and SATT pulses, and detect class of service pulses appearing simultaneously with SATT pulses.